rp can not renew unless person is in qtr.your case is very simple.get new baby(mabrook),make new passport of baby.your family have already rp number in qtr(I hope they were in qtr)apply again in labour dept(follow requirements)same time apply for new baby s visa. babies birth certificate shoud be attested from authority.its same like new visa but since your family have rp number,so it will be easy to get visa.
good luck